1. Field of the Invention
The present invention relates to a graphite-containing conductive suspension for making contact to the inside of a picture tube.
2. Description of the Prior Art
It is known that inside a picture tube, electric contact must be made between an aluminum film deposited on the panel by evaporation, a graphite coating on the inner sidewalls of the picture tube, and the anode contact sealed in the end of the tube neck. Such electric contacts are usually made during the fabrication of the picture tube by applying a graphite suspension to produce contact lines at the inner rim of the screen and a contact ring in the tube neck. The graphite suspension can be applied by printing, spraying, or with a brush, for example. After the contact lines have been applied to the inside of the screen, an aluminum film is deposited by evaporation in a high vacuum.
Before the funnel and the panel are joined together, the tube must be baked out to remove the organic ingredients. A solder-glass paste is applied to the edges of the panel and the funnel, and the two parts are fused together by hot sealing. This is usually followed by another bakeout process.
These known process steps for making picture tubes are described, for example, in the journal Funk-Technik, 1967, No. 15, pp. 576 to 580.
The graphite suspension commonly used to produce the electric connections inside the picture tube is a mixture of graphite and water glass. With this mixture, sufficient electric contact is achieved, but this suspension has the disadvantage of being impermeable to organic substances after hardening, so that organic substances below the conductive coating cannot be removed by bakeout. Therefore, the contact lines must be applied prior to the deposition of the aluminum film, or the aluminum film must be baked out before the contact lines are applied.
In addition, the known conductive suspension has the disadvantage of being difficult to remove from the glass parts of the tube, thus complicating the reuse of defective tube parts.